Remove classifier for Python 3.4 for end-of-life. (#7535)

* Remove classifier for Python 3.4 for end-of-life.

* Update supported versions in Client README, Contributing Guide

Author: crwilcox

packages/google-cloud-bigquery-datatransfer/README.rst

@@ -48,7 +48,7 @@ dependencies.
 
 Supported Python Versions
 ^^^^^^^^^^^^^^^^^^^^^^^^^
-Python >= 3.4
+Python >= 3.5
 
 Deprecated Python Versions
 ^^^^^^^^^^^^^^^^^^^^^^^^^^

packages/google-cloud-bigquery-datatransfer/setup.py

@@ -72,7 +72,6 @@
         'Programming Language :: Python :: 2',
         'Programming Language :: Python :: 2.7',
         'Programming Language :: Python :: 3',
-        'Programming Language :: Python :: 3.4',
         'Programming Language :: Python :: 3.5',
         'Programming Language :: Python :: 3.6',
         'Programming Language :: Python :: 3.7',